One type of tie of subsea well employs a wellhead housing located at the sea floor and a drilling blowout preventer or production Christmas tree located at the surface on a platform. Large diameter casing will be lowered from the platform and connected to the wellhead housing with a tieback connecter. The tieback connector must withstand various loading conditions it may see during extended operation. Particularly with a tensioned leg or spar platform where the upper end of the riser is permitted to move horizontally, a bending moment is produced at the wellhead. This may occur even with a fixed platform where there is significant current force acting on the riser. The connection to the wellhead must also be capable of carrying substantial vertical force either in compression where insufficient load is carried by the platform or in tension where excessive load is carried by the platform. Thermal expansion of various components of this structure also occurs, depending on whether or not the well is producing at a particular time and the temperature of the fluid being produced. Furthermore, the riser must endure these stresses through many cycles over many years.
One type of connector has a downward facing funnel that slides over the wellhead housing. It has a body with a connector device which contacts grooves or threads formed on the wellhead housing. A running tool or internal hydraulic cylinders actuate the connector device and joins the riser and wellhead housing. The connector is locked in this position by bolts and various other bolts are in the load path. When released, this type of tieback connector does not have a mechanism to actively release the connector device from the wellhead grooves.
While successful, improvements are desired for tieback connectors wherein large bending forces may be exerted, such as with tension leg platforms or spars.